Synergistic Suppression of NF1 Malignant Peripheral Nerve Sheath Tumor Cell Growth in Culture and Orthotopic Xenografts by Combinational Treatment with Statin and Prodrug Farnesyltransferase Inhibitor PAMAM G4 Dendrimers

Neurofibromatosis type 1 (NF1) is a disorder in which RAS is constitutively activated due to the loss of the Ras-GTPase-activating activity of neurofibromin. RAS must be prenylated (i.e., farnesylated or geranylgeranylated) to traffic and function properly. Previous studies showed that the anti-growth properties of farnesyl monophosphate prodrug farnesyltransferase inhibitors (FTIs) on human NF1 malignant peripheral nerve sheath tumor (MPNST) cells are potentiated by co-treatment with lovastatin. Unfortunately, such prodrug FTIs have poor aqueous solubility. In this study, we synthesized a series of prodrug FTI polyamidoamine generation 4 (PAMAM G4) dendrimers that compete with farnesyl pyrophosphate for farnesyltransferase (Ftase) and assessed their effects on human NF1 MPNST S462TY cells. The prodrug 3-tert-butylfarnesyl monophosphate FTI-dendrimer (i.e., IG 2) exhibited improved aqueous solubility. Concentrations of IG 2 and lovastatin (as low as 0.1 μM) having little to no effect when used singularly synergistically suppressed cell proliferation, colony formation, and induced N-RAS, RAP1A, and RAB5A deprenylation when used in combination. Combinational treatment had no additive or synergistic effects on the proliferation/viability of immortalized normal rat Schwann cells, primary rat hepatocytes, or normal human mammary epithelial MCF10A cells. Combinational, but not singular, in vivo treatment markedly suppressed the growth of S462TY xenografts established in the sciatic nerves of immune-deficient mice. Hence, prodrug farnesyl monophosphate FTIs can be rendered water-soluble by conjugation to PAMAM G4 dendrimers and exhibit potent anti-tumor activity when combined with clinically achievable statin concentrations.

At low levels, inorganic mercury interference with antigen signaling is associated with modifications to a panel of novel phosphoserine sites in B cell receptor pathway proteins

Epidemiological studies indicate that human and animal exposure to environmental mercury (Hg) disrupts normal immune system function, but the molecular mechanism responsible for this is still unresolved. We have previously utilized phospho-proteomic mass spectrometry to demonstrate that in the absence of B Cell Receptor (BCR) stimulation, exposure of B cells to Hg induces significant changes to a great many elements of the BCR signaling pathway in a concentration dependent manner. In this report, we have extended those initial findings by utilizing mass spectrometry to evaluate in detail the effect of low-level Hg exposure on BCR induced phospho-proteomic changes. Specifically, murine WEHI-231 B lymphoma cells were exposed to environmentally relevant levels of Hg with or without concomitant BCR stimulation. The cellular phospho-proteomes were then profiled by LC-MS/MS. We found that for low-level exposures, Hg interference with signal transduction across the BCR pathway was predominantly associated with modification of phosphorylation of 12 phosphosites located on seven different proteins. Nine sites were serine, two sites tyrosine and one site threonine. Most of these sites are novel, in the sense that only the two tyrosine and one of the serine sites have previously been reported to be associated with BCR signaling.

Ang II acutely stimulates Na,K-pump in cells from proximal tubules by increasing its phosphorylation at S938 via a PI3K/AKT pathway

Angiotensin II (Ang II)-dependent stimulation of the AT1 receptor in proximal tubules increases sodium reabsorption and blood pressure. Reabsorption is driven by the Na,K-pump that is acutely stimulated by Ang II, which requires phosphorylation of serine-938 (S938). This site is present in humans and only known to phosphorylated by PKA. Yet, activation of AT1 decreases cAMP required to activate PKA and inhibiting PKA does not block Ang II-dependent phosphorylation of S938. We tested the hypothesis that Ang II-dependent activation is mediated via increased phosphorylation at S938 through a PI3K/AKT-dependent pathway. Experiments were conducted using opossum kidney cells, a proximal tubule cell line, stably co-expressing the AT1 receptor and either the wild-type (α-1.wild-type) or an alanine substituted (α-1.S938A) form of rat kidney Na,K-pump. A 5-min exposure to 10 pM Ang II significantly activated Na,K-pump activity (56%) measured as short-circuit current across polarized α-1.wild-type cells. Wortmannin, at a concentration that selectively inhibits PI3K, blocked that Ang II-dependent activation. Ang II did not stimulate Na,K-pump activity in α-1.S938A cells. Ang II at 10 and 100 pM increased phosphorylation at S938 in α-1.wild-type cells measured in whole cell lysates. The increase was inhibited by wortmannin plus H-89, an inhibitor of PKA, not by either alone. Ang II activated AKT inhibited by wortmannin, not H-89. These data support our hypothesis and show that Ang II-dependent phosphorylation at S938 stimulates Na,K-pump activity and transcellular sodium transport.

Sprouty4 negatively regulates ERK/MAPK signaling and the transition from in situ to invasive breast ductal carcinoma

Breast ductal carcinoma in situ (DCIS) is a non-obligate precursor of invasive ductal carcinoma (IDC). It is still unclear which DCIS will become invasive and which will remain indolent. Patients often receive surgery and radiotherapy, but this early intervention has not produced substantial decreases in late-stage disease. Sprouty proteins are important regulators of ERK/MAPK signaling and have been studied in various cancers. We hypothesized that Sprouty4 is an endogenous inhibitor of ERK/MAPK signaling and that its loss/reduced expression is a mechanism by which DCIS lesions progress toward IDC, including triple-negative disease. Using immunohistochemistry, we found reduced Sprouty4 expression in IDC patient samples compared to DCIS, and that ERK/MAPK phosphorylation had an inverse relationship to Sprouty4 expression. These observations were reproduced using a 3D culture model of disease progression. Knockdown of Sprouty4 in MCF10.DCIS cells increased ERK/MAPK phosphorylation as well as their invasive capability, while overexpression of Sprouty4 in MCF10.CA1d IDC cells reduced ERK/MAPK phosphorylation, invasion, and the aggressive phenotype exhibited by these cells. Immunofluorescence experiments revealed reorganization of the actin cytoskeleton and relocation of E-cadherin back to the cell surface, consistent with the restoration of adherens junctions. To determine whether these effects were due to changes in ERK/MAPK signaling, MEK1/2 was pharmacologically inhibited in IDC cells. Nanomolar concentrations of MEK162/binimetinib restored an epithelial-like phenotype and reduced pericellular proteolysis, similar to Sprouty4 overexpression. From these data we conclude that Sprouty4 acts to control ERK/MAPK signaling in DCIS, thus limiting the progression of these premalignant breast lesions.

In Vitro Models for Studying Invasive Transitions of Ductal Carcinoma In Situ

About one fourth of all newly identified cases of breast carcinoma are diagnoses of breast ductal carcinoma in situ (DCIS). Since we cannot yet distinguish DCIS cases that would remain indolent from those that may progress to life-threatening invasive ductal carcinoma (IDC), almost all women undergo aggressive treatment. In order to allow for more rational individualized treatment, we and others are developing in vitro models to identify and validate druggable pathways that mediate the transition of DCIS to IDC. These models range from conventional two-dimensional (2D) monolayer cultures on plastic to 3D cultures in natural or synthetic matrices. Some models consist solely of DCIS cells, either cell lines or primary cells. Others are co-cultures that include additional cell types present in the normal or cancerous human breast. The 3D co-culture models more accurately mimic structural and functional changes in breast architecture that accompany the transition of DCIS to IDC. Mechanistic studies of the dynamic and temporal changes associated with this transition are facilitated by adapting the in vitro models to engineered microfluidic platforms. Ultimately, the goal is to create in vitro models that can serve as a reproducible preclinical screen for testing therapeutic strategies that will reduce progression of DCIS to IDC. This review will discuss the in vitro models that are currently available, as well as the progress that has been made using them to understand DCIS pathobiology.

Breast Cancer: Proteolysis and Migration

Understanding breast cancer cell proteolysis and migration is crucial for developing novel therapies to prevent local and distant metastases. Human cancer cells utilize many biological functions comparable to those observed during embryogenesis conferring the cancer cells with survival advantages. One such advantage is the ability to secrete proteases into the tumor microenvironment in order to remodel the extracellular matrix to facilitate migration. These proteases degrade the extracellular matrix, which initially functions as a barrier to cancer cell escape from their site of origin. The extracellular matrix also functions as a reservoir for growth factors that can be released by the secreted proteases and thereby further aid tumor growth and progression. Other survival advantages of tumor cells include: the ability to utilize multiple modes of motility, thrive in acidic microenvironments, and the tumor cell's ability to hijack stromal and immune cells to foster their own migration and survival. In order to reduce metastasis, we must focus our efforts on addressing the survival advantages that tumor cells have acquired.

Downregulation of Rap1Gap: A Switch from DCIS to Invasive Breast Carcinoma via ERK/MAPK Activation

Diagnosis of breast ductal carcinoma in situ (DCIS) presents a challenge since we cannot yet distinguish those cases that would remain indolent and not require aggressive treatment from cases that may progress to invasive ductal cancer (IDC). The purpose of this study is to determine the role of Rap1Gap, a GTPase activating protein, in the progression from DCIS to IDC. Immunohistochemistry (IHC) analysis of samples from breast cancer patients shows an increase in Rap1Gap expression in DCIS compared to normal breast tissue and IDCs. In order to study the mechanisms of malignant progression, we employed an in vitro three-dimensional (3D) model that more accurately recapitulates both structural and functional cues of breast tissue. Immunoblotting results show that Rap1Gap levels in MCF10.Ca1D cells (a model of invasive carcinoma) are reduced compared to those in MCF10.DCIS (a model of DCIS). Retroviral silencing of Rap1Gap in MCF10.DCIS cells activated extracellular regulated kinase (ERK) mitogen-activated protein kinase (MAPK), induced extensive cytoskeletal reorganization and acquisition of mesenchymal phenotype, and enhanced invasion. Enforced reexpression of Rap1Gap in MCF10.DCIS-Rap1GapshRNA cells reduced Rap1 activity and reversed the mesenchymal phenotype. Similarly, introduction of dominant negative Rap1A mutant (Rap1A-N17) in DCIS-Rap1Gap shRNA cells caused a reversion to nonmalignant phenotype. Conversely, expression of constitutively active Rap1A mutant (Rap1A-V12) in noninvasive MCF10.DCIS cells led to phenotypic changes that were reminiscent of Rap1Gap knockdown. Thus, reduction of Rap1Gap in DCIS is a potential switch for progression to an invasive phenotype. The Graphical Abstract summarizes these findings.

Abstract B14: Sprouty4 regulates the transition to invasive breast ductal carcinoma through ERK/MAPK signaling

Breast cancer is one of the most common oncologic developments in U.S. women, with approximately 25% of these cases being in situ disease (DCIS). For many years DCIS lesions have been treated using surgery and radiotherapy with the goal of decreasing the amount of late-stage disease. Unfortunately, a number of reports have since shown that early intervention is not sufficient and have highlighted the likelihood of overtreatment. This is especially true for triple-negative breast cancers, which are more strongly associated with distant recurrence, metastasis, and death compared to other types of invasive breast ductal carcinoma (IDC). These factors have generated a substantial clinical need for reliable biomarkers or molecular determinants to assess disease progression. Sprouty proteins are recognized as important regulators of ERK/MAPK signaling, and have been studied in various cancers. We hypothesize that Sprouty4 is an endogenous inhibitor of ERK/MAPK signaling, and its loss or reduced expression is a mechanism by which DCIS lesions progress toward IDC, including triple-negative disease. Using immunohistochemistry we found that Sprouty4 expression was reduced in IDC patient tissue samples compared to normal or DCIS tissues, and that ERK/MAPK activity had an inverse relationship to Sprouty4 expression. These results correspond with immunoblot data from our 3D culture model of breast cancer progression in which Sprouty4 expression was higher during DCIS than in the IDC stage. Efficient overexpression of Sprouty4 reduced both ERK/MAPK activity as well as the aggressive phenotype of MCF10.CA1d IDC cells. Immunofluorescence experiments revealed data consistent with the relocation of E-cadherin back to the cell surface and the restoration of adherens junctions. To determine whether these effects were due to changes in ERK/MAPK signaling, IDC cells were treated with MEK162, an allosteric MEK inhibitor. Nanomolar concentrations of drug produced the restoration of an epithelial-like phenotype similar to Sprouty4 overexpression. From these data we conclude that Sprouty4 may act to control ERK/MAPK signaling in DCIS, thus limiting the progression of these premalignant breast lesions.

Citation Format: Ethan J. Brock, Ryan Jackson, Julie L. Boerner, Quanwen Li, Bonnie F. Sloane, Raymond R. Mattingly. Sprouty4 regulates the transition to invasive breast ductal carcinoma through ERK/MAPK signaling [abstract]. In: Proceedings of the AACR Special Conference: Advances in Breast Cancer Research; 2017 Oct 7-10; Hollywood, CA. Philadelphia (PA): AACR; Mol Cancer Res 2018;16(8_Suppl):Abstract nr B14.

Abstract 2131: Paracrine cytokine pathways mediate metastasis of breast cancer to lymphatics

Lymphatics, rather than blood vessels, are the primary route for breast cancer metastasis. The presence of breast cancer cells in regional lymphatics, i.e., lymphatic metastasis, is an important prognostic factor for patients. Delineating molecular mechanisms by which the breast cancer cells migrate toward and infiltrate into lymphatics is crucial to designing new therapies to prevent metastatic dissemination. To study tumor:lymphatic interactions, we are using a three-dimensional (3D) heterotypic co-culture model of human breast cancer cells (hBCCs) grown with human microvascular lymphatic endothelial cells (hLECs) in novel chambers that we designed and fabricated. These chambers support growth of the 3D co-cultures, live-cell confocal imaging in real time and noninvasive collection of conditioned media for secretomic analyses. We use live-cell assays developed in our laboratory for quantitative analysis of temporal and dynamic changes in BCC:LEC interactions in correspondence with changes in their malignant and proteolytic phenotypes. We cultured hLECs in the presence and absence of human MDA-MB-231 (231) triple-negative BCCs in 3D cultures for 4 days. In mono-cultures, the 231 cells grow in clusters that exhibit a stellate morphology and hLECs form branching networks with central nodes. We observed that the volumes of 3D structures formed by LECs and 231 cells were significantly greater in co-cultures than in mono-cultures of either cell type. In addition, 231 cells infiltrate into the LEC networks with the infiltration increasing over the 4-day period as assessed by the degree of overlap between 231 cells and hLECs in 3D reconstructions of the co-cultures. Moreover, soluble factors from LECs increase invasive outgrowths of 231 structures. This was demonstrated in 231 cells grown in media conditioned by LECs and in parallel co-cultures of 231 cells and LECs. The induction of invasiveness by LEC conditioned media is reduced by boiling and repeated freeze/thawing, suggesting that the active factor(s) is a protein. Our preliminary results suggest that LECs secrete soluble factors that may be therapeutic targets for reducing invasion of BCCs into lymphatic networks.

Citation Format: Kyungmin Ji, Zhiguo Zhao, Kamiar Moin, Yong Xu, Robert J. Gillies, Raymond R. Mattingly, Bonnie F. Sloane. Paracrine cytokine pathways mediate metastasis of breast cancer to lymphatics [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2131.

Ras and Rap1: A tale of two GTPases

Ras oncoproteins play pivotal roles in both the development and maintenance of many tumor types. Unfortunately, these proteins are difficult to directly target using traditional pharmacological strategies, in part due to their lack of obvious binding pockets or allosteric sites. This obstacle has driven a considerable amount of research into pursuing alternative ways to effectively inhibit Ras, examples of which include inducing mislocalization to prevent Ras maturation and inactivating downstream proteins in Ras-driven signaling pathways. Ras proteins are archetypes of a superfamily of small GTPases that play specific roles in the regulation of many cellular processes, including vesicle trafficking, nuclear transport, cytoskeletal rearrangement, and cell cycle progression. Several other superfamily members have also been linked to the control of normal and cancer cell growth and survival. For example, Rap1 has high sequence similarity to Ras, has overlapping binding partners, and has been demonstrated to both oppose and mimic Ras-driven cancer phenotypes. Rap1 plays an important role in cell adhesion and integrin function in a variety of cell types. Mechanistically, Ras and Rap1 cooperate to initiate and sustain ERK signaling, which is activated in many malignancies and is the target of successful therapeutics. Here we review the role activated Rap1 in ERK signaling and other downstream pathways to promote invasion and cell migration and metastasis in various cancer types.

Development of 3D culture models of plexiform neurofibroma and initial application for phenotypic characterization and drug screening

Plexiform neurofibromas (PNs), which may be present at birth in up to half of children with type 1 neurofibromatosis (NF1), can cause serious loss of function, such as quadriparesis, and can undergo malignant transformation. Surgery is the first line treatment although the invasive nature of these tumors often prevents complete resection. Recent clinical trials have shown promising success for some drugs, notably selumetinib, an inhibitor of MAP kinase kinase (MEK). We have developed three-dimensional (3D) cell culture models of immortalized cells from NF1 PNs and of control Schwann cells (SCs) that we believe mimic more closely the in vivo condition than conventional two-dimensional (2D) cell culture. Our goal is to facilitate pre-clinical identification of potential targeted therapeutics for these tumors. Three drugs, selumetinib (a MEK inhibitor), picropodophyllin (an IGF-1R inhibitor) and LDN-193189 (a BMP2 inhibitor) were tested with dose-response design in both 2D and 3D cultures for their abilities to block net cell growth. Cell lines grown in 3D conditions showed varying degrees of resistance to the inhibitory actions of all three drugs. For example, control SCs became resistant to growth inhibition by selumetinib in 3D culture. LDN-193189 was the most effective drug in 3D cultures, with only slightly reduced potency compared to the 2D cultures. Characterization of these models also demonstrated increased proteolysis of collagen IV in the matrix by the PN driver cells as compared to wild-type SCs. The proteolytic capacity of the PN cells in the model may be a clinically significant property that can be used for testing the ability of drugs to inhibit their invasive phenotype.

Pathomimetic avatars reveal divergent roles of microenvironment in invasive transition of ductal carcinoma in situ

BACKGROUND

The breast tumor microenvironment regulates progression of ductal carcinoma in situ (DCIS) to invasive ductal carcinoma (IDC). However, it is unclear how interactions between breast epithelial and stromal cells can drive this progression and whether there are reliable microenvironmental biomarkers to predict transition of DCIS to IDC.

METHODS

We used xenograft mouse models and a 3D pathomimetic model termed mammary architecture and microenvironment engineering (MAME) to study the interplay between human breast myoepithelial cells (MEPs) and cancer-associated fibroblasts (CAFs) on DCIS progression.

RESULTS

Our results show that MEPs suppress tumor formation by DCIS cells in vivo even in the presence of CAFs. In the in vitro MAME model, MEPs reduce the size of 3D DCIS structures and their degradation of extracellular matrix. We further show that the tumor-suppressive effects of MEPs on DCIS are linked to inhibition of urokinase plasminogen activator (uPA)/urokinase plasminogen activator receptor (uPAR)-mediated proteolysis by plasminogen activator inhibitor 1 (PAI-1) and that they can lessen the tumor-promoting effects of CAFs by attenuating interleukin 6 (IL-6) signaling pathways.

CONCLUSIONS

Our studies using MAME are, to our knowledge, the first to demonstrate a divergent interplay between MEPs and CAFs within the DCIS tumor microenvironment. We show that the tumor-suppressive actions of MEPs are mediated by PAI-1, uPA and its receptor, uPAR, and are sustained even in the presence of the CAFs, which themselves enhance DCIS tumorigenesis via IL-6 signaling. Identifying tumor microenvironmental regulators of DCIS progression will be critical for defining a robust and predictive molecular signature for clinical use.

Abstract B28: Induced expression of Sprouty4 in breast invasive ductal carcinoma cells inhibits ERK MAP kinase and reduces malignant phenotype

Our previous work has identified increased expression of Sprouty4 in 3D models of breast ductal carcinoma in situ (DCIS). Sprouty4 in other systems has been shown to function as a negative regulator of the mitogen activated protein kinase (MAPK/ERK) pathway. We hypothesize that Sprouty4 is an endogenous inhibitor of ERK/MAPK signaling in DCIS, and that its loss or reduced expression is one mechanism by which triple-negative lesions progress toward invasive ductal carcinoma (IDC). Using immunohistochemistry our labs have found that Sprouty4 was highly expressed in some human premalignant breast tissue samples, and that this expression was reduced in malignant triple-negative samples. These results correspond with immunoblot data from our 3D culture model of breast cancer progression in which Sprouty4 expression was higher during DCIS than in the IDC stage. Efficient over-expression of Sprouty4 reduced both MAPK/ERK activity as well as the aggressive phenotype of MCF10.CA1d IDC cells. Immunofluorescence experiments done in IDC cells overexpressing Sprouty4 revealed relocation of E-cadherin back to the cell surface and the restoration of adherens junctions. To determine if these effects were due to changes in MAPK/ERK signaling, IDC cells were treated with MEK162, an allosteric MEK inhibitor. Nanomolar concentrations of drug restored an epithelial-like phenotype similar to that produced by Sprouty4 over-expression. From these data we conclude that Sprouty4 may act to control MAPK/ERK signaling in a subset of DCIS, thus limiting the progression of these premalignant breast cancers. Further, if in vivo data correspond with our in vitro work, this may argue for the investigation of MEK inhibitors as an adjunct treatment in triple-negative disease, where options are limited.

Citation Format: Ryan M. Jackson, Ethan J. Brock, Seema Shah, Mansoureh Sameni, Bonnie F. Sloane, Quanwen Li, Raymond R. Mattingly. Induced expression of Sprouty4 in breast invasive ductal carcinoma cells inhibits ERK MAP kinase and reduces malignant phenotype. [abstract]. In: Proceedings of the AACR Precision Medicine Series: Targeting the Vulnerabilities of Cancer; May 16-19, 2016; Miami, FL. Philadelphia (PA): AACR; Clin Cancer Res 2017;23(1_Suppl):Abstract nr B28.

How to Target Activated Ras Proteins: Direct Inhibition vs. Induced Mislocalization

Oncogenic Ras proteins are a driving force in a significant set of human cancers and wildtype, unmutated Ras proteins likely contribute to the malignant phenotype of many more. The overall challenge of targeting activated Ras proteins has great promise to treat cancer, but this goal has yet to be achieved. Significant efforts and resources have been committed to inhibiting Ras, but these energies have so far made little impact in the clinic. Direct attempts to target activated Ras proteins have faced many obstacles, including the fundamental nature of the gain-of-function oncogenic activity being produced by a loss-of-function at the biochemical level. Nevertheless, there has been very promising recent pre-clinical progress. The major strategy that has so far reached the clinic aimed to inhibit activated Ras indirectly through blocking its post-translational modification and inducing its mislocalization. While these efforts to indirectly target Ras through inhibition of farnesyl transferase (FTase) were rationally designed, this strategy suffered from insufficient attention to the distinctions between the isoforms of Ras. This led to subsequent failures in large-scale clinical trials targeting K-Ras driven lung, colon, and pancreatic cancers. Despite these setbacks, efforts to indirectly target activated Ras through inducing its mislocalization have persisted. It is plausible that FTase inhibitors may still have some utility in the clinic, perhaps in combination with statins or other agents. Alternative approaches for inducing mislocalization of Ras through disruption of its palmitoylation cycle or interaction with chaperone proteins are in early stages of development.

Abstract 4560: Induced Sprouty4 expression in breast invasive ductal carcinoma cells downregulates ERK/MAPK activity and restores an epithelial-like phenotype

Breast cancer is one of the most common cancers in U.S. women, with approximately 25% of these cases being in situ disease. Sprouty proteins are currently recognized as important regulators of ERK/MAPK signaling, and have been studied in various cancer types. By employing RNA-seq, previous studies from our laboratories determined specific gene expression changes common to three models of ductal carcinoma in situ (DCIS)—MCF10.DCIS, SUM 102, and SUM 225—when compared to MCF10A cells (a model of non-transformed breast epithelium). All cell lines were grown in three-dimensional (3D) reconstituted basement membrane overlay culture because research has shown that the behavior of cancer cells in 3D matrices is more reflective of an in vivo response when exposed to drugs and radiotherapy than if they are cultured on plastic. Among the three models of DCIS, 63 genes were consistently upregulated. We identified 244 promoters associated with these 63 genes and performed bioinformatic data mining that revealed a high level of enrichment for a promoter framework shared by three of these genes: one of which encoded for the protein Sprouty4. We hypothesize that Sprouty4 is an endogenous inhibitor of ERK/MAPK signaling in DCIS, and its loss or reduced expression is a mechanism by which triple-negative lesions progress toward invasive ductal carcinoma (IDC). Using immunohistochemistry we found that Sprouty4 was highly expressed in certain human premalignant breast tissue samples, and that this expression was reduced in malignant triple-negative samples. These results correspond with immunoblot data from our 3D culture model of breast cancer progression in which Sprouty4 expression was higher during DCIS than in the IDC stage. Efficient over-expression of Sprouty4 reduced both ERK/MAPK activity as well as the aggressive phenotype of MCF10.CA1d IDC cells. Immunofluorescence experiments revealed data consistent with the relocation of E-cadherin back to the cell surface and the restoration of adherens. To determine if these effects were due to changes in ERK/MAPK signaling IDC cells were treated with MEK162, an allosteric MEK inhibitor. Nanomolar concentrations of drug produced a restoration of an epithelial-like phenotype similar to Sprouty4 over-expression. From these data we conclude that Sprouty4 may act to control ERK/MAPK signaling in a subset of DCIS, thus limiting the progression of these premalignant breast cancers.

Citation Format: Ethan J. Brock, Ryan Jackson, Seema Shah, Quanwen Li, Mansoureh Sameni, Stephen A. Krawetz, Shihong Mao, Bonnie F. Sloane, Raymond R. Mattingly. Induced Sprouty4 expression in breast invasive ductal carcinoma cells downregulates ERK/MAPK activity and restores an epithelial-like phenotype. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4560.

Phosphorylation of rat kidney Na-K pump at Ser938 is required for rapid angiotensin II-dependent stimulation of activity and trafficking in proximal tubule cells

How angiotensin (ANG) II acutely stimulates the Na-K pump in proximal tubules is only partially understood, limiting insight into how ANG II increases blood pressure. First, we tested whether ANG II increases the number of pumps in plasma membranes of native rat proximal tubules under conditions of rapid activation. We found that exposure to 100 pM ANG II for 2 min, which was previously shown to increase affinity of the Na-K pump for Na and stimulate activity threefold, increased the amount of the Na-K pump in plasma membranes of native tubules by 33%. Second, we tested whether previously observed increases in phosphorylation of the Na-K pump at Ser(938) were part of the stimulatory mechanism. These experiments were carried out in opossum kidney cells, cultured proximal tubules stably coexpressing the ANG type 1 (AT1) receptor, and either wild-type or a S938A mutant of rat kidney Na-K pump under conditions found by others to stimulate activity. We found that 10 min of incubation in 10 pM ANG II stimulated activity of wild-type pumps from 2.3 to 3.5 nmol K · mg protein(-1) · min(-1) and increased the amount of the pump in the plasma membrane by 80% but had no effect on cells expressing the S938A mutant. We conclude that acute stimulation of Na-K pump activity in native rat proximal tubules includes increased trafficking to the plasma membrane and that phosphorylation at Ser(938) is part of the mechanism by which ANG II directly stimulates activity and trafficking of the rat kidney Na-K pump in opossum kidney cells.

Il-6 signaling between ductal carcinoma in situ cells and carcinoma-associated fibroblasts mediates tumor cell growth and migration

Background

Ductal carcinoma in situ (DCIS) is a non-obligate precursor lesion of invasive breast cancer in which approximately half the patients will progress to invasive cancer. Gaining a better understanding of DCIS progression may reduce overtreatment of patients. Expression of the pro-inflammatory cytokine interleukin-6 increases with pathological stage and grade, and is associated with poorer prognosis in breast cancer patients. Carcinoma associated fibroblasts (CAFs), which are present in the stroma of DCIS patients are known to secrete pro-inflammatory cytokines and promote tumor progression.

Methods

We hypothesized that IL-6 paracrine signaling between DCIS cells and CAFs mediates DCIS proliferation and migration. To test this hypothesis, we utilized the mammary architecture and microenvironment engineering or MAME model to study the interactions between human breast CAFs and human DCIS cells in 3D over time. We specifically inhibited autocrine and paracrine IL-6 signaling to determine its contribution to early stage tumor progression.

Results

Here, DCIS cells formed multicellular structures that exhibited increased proliferation and migration when cultured with CAFs. Treatment with an IL-6 neutralizing antibody inhibited growth and migration of the multicellular structures. Moreover, selective knockdown of IL-6 in CAFs, but not in DCIS cells, abrogated the migratory phenotype.

Conclusion

Our results suggest that paracrine IL-6 signaling between preinvasive DCIS cells and stromal CAFs represent an important factor in the initiation of DCIS progression to invasive breast carcinoma.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-015-1576-3) contains supplementary material, which is available to authorized users.

Abstract 3150: Exploring the role of Rap1Gap in the progression from DCIS to invasive breast carcinoma

Understanding the underlying mechanisms that drive malignant progression of breast cancer is important. The purpose of this study is to define the role of Rap1Gap in the progression of ductal carcinoma in-situ (DCIS) to invasive cancer. We employed an in-vitro three-dimensional (3D) overlay model that provides a physiologically relevant microenvironment to study mechanisms of mammary gland development and malignant progression. We previously employed next generation sequencing (NGS) and identified 63 consistently upregulated genes in three DCIS lines (SUM102, SUM225, MCF10.DCIS) compared to non-transformed mammary epithelial cells. To gain insight into common transcriptional elements of co-regulated genes that may be critical to the DCIS phenotype, we have mined our NGS data using Frameworker (Genomatix). The 63 upregulated genes are associated with 244 candidate promoters out of a total of 82,703 promoters in the entire human genome. Our analysis shows that the common framework RXRF-ZF02-ZF02-PLAG-HDBP is only present in the promoters of three genes: RAP1GAP, SPRY4 and PDGFB. All of these genes are upregulated in our DCIS signature, which means that this framework is hugely enriched (336-fold) over what would be expected by chance. Rap1Gap has tumor suppressor properties; its functions, via regulation of Rap1 activity, include regulation of cell adhesion, suppression of cell proliferation and metastasis. In other epithelial cancers, loss of Rap1Gap has been linked to epithelial to mesenchymal transition (EMT) and invasion. To begin study of Rap1Gap in breast cancer progression, we performed immunohistochemistry. We show strong Rap1Gap staining in DCIS with little to no expression in myoepithelial and stromal components. Immunoblotting results show that Rap1Gap levels in MCF10.CA1d cells (a model of invasive carcinoma) are reduced compared to those in MCF10.DCIS cells. Rap1Gap expression is low in additional basal breast cancer cell lines, but high in luminal ER+ /PR+ cell lines. We propose that over-expression of Rap1Gap may serve as a tumor suppressive mechanism in DCIS; subsequent reduction of Rap1Gap may be a switch for EMT and progression to an invasive phenotype.

Citation Format: Seema Shah, Kingsley Osuala, Shihong Mao, Quanwen Li, Bonnie Sloane, Stephen Krawetz, Raymond R. Mattingly. Exploring the role of Rap1Gap in the progression from DCIS to invasive breast carcinoma. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3150. doi:10.1158/1538-7445.AM2014-3150

Abrogating phosphorylation of eIF4B is required for EGFR and mTOR inhibitor synergy in triple-negative breast cancer

Triple-negative breast cancer (TNBC) patients suffer from a highly malignant and aggressive disease. They have a high rate of relapse and often develop resistance to standard chemotherapy. Many TNBCs have elevated epidermal growth factor receptor (EGFR) but are resistant to EGFR inhibitors as monotherapy. In this study, we sought to find a combination therapy that could sensitize TNBC to EGFR inhibitors. Phospho-mass spectrometry was performed on the TNBC cell line, BT20, treated with 0.5 μM gefitinib. Immunoblotting measured protein levels and phosphorylation. Colony formation and growth assays analyzed the treatment on cell proliferation, while MTT assays determined the synergistic effect of inhibitor combination. A Dual-Luciferase reporter gene plasmid measured translation. All statistical analysis was done on CalucuSyn and GraphPad Prism using ANOVAs. Phospho-proteomics identified the mTOR pathway to be of interest in EGFR inhibitor resistance. In our studies, combining gefitinib and temsirolimus decreased cell growth and survival in a synergistic manner. Our data identified eIF4B, as a potentially key fragile point in EGFR and mTOR inhibitor synergy. Decreased eIF4B phosphorylation correlated with drops in growth, viability, clonogenic survival, and cap-dependent translation. Taken together, these data suggest EGFR and mTOR inhibitors abrogate growth, viability, and survival via disruption of eIF4B phosphorylation leading to decreased translation in TNBC cell lines. Further, including an mTOR inhibitor along with an EGFR inhibitor in TNBC with increased EGFR expression should be further explored. Additionally, translational regulation may play an important role in regulating EGFR and mTOR inhibitor synergy and warrant further investigation.

Next-generation sequencing: a powerful tool for the discovery of molecular markers in breast ductal carcinoma in situ

Mammographic screening leads to frequent biopsies and concomitant overdiagnosis of breast cancer, particularly ductal carcinoma in situ (DCIS). Some DCIS lesions rapidly progress to invasive carcinoma, whereas others remain indolent. Because we cannot yet predict which lesions will not progress, all DCIS is regarded as malignant, and many women are overtreated. Thus, there is a pressing need for a panel of molecular markers in addition to the current clinical and pathological factors to provide prognostic information. Genomic technologies such as microarrays have made major contributions to defining subtypes of breast cancer. Next-generation sequencing (NGS) modalities offer unprecedented depth of expression analysis through revealing transcriptional boundaries, mutations, rare transcripts and alternative splice variants. NGS approaches are just beginning to be applied to DCIS. Here, the authors review the applications and challenges of NGS in discovering novel potential therapeutic targets and candidate biomarkers in the premalignant progression of breast cancer.

Tyrosyl phosphorylated PAK1 regulates breast cancer cell motility in response to prolactin through filamin A

The p21-activated serine-threonine kinase (PAK1) is activated by small GTPase-dependent and -independent mechanisms and regulates cell motility. Both PAK1 and the hormone prolactin (PRL) have been implicated in breast cancer by numerous studies. We have previously shown that the PRL-activated tyrosine kinase JAK2 (Janus tyrosine kinase 2) phosphorylates PAK1 in vivo and identified tyrosines (Tyr) 153, 201, and 285 in the PAK1 molecule as sites of JAK2 tyrosyl phosphorylation. Here, we have used human breast cancer T47D cells stably overexpressing PAK1 wild type or PAK1 Y3F mutant in which Tyr(s) 153, 201, and 285 were mutated to phenylalanines to demonstrate that phosphorylation of these three tyrosines are required for maximal PRL-dependent ruffling. In addition, phosphorylation of these three tyrosines is required for increased migration of T47D cells in response to PRL as assessed by two independent motility assays. Finally, we show that PAK1 phosphorylates serine (Ser) 2152 of the actin-binding protein filamin A to a greater extent when PAK1 is tyrosyl phosphorylated by JAK2. Down-regulation of PAK1 or filamin A abolishes the effect of PRL on cell migration. Thus, our data presented here bring some insight into the mechanism of PRL-stimulated motility of breast cancer cells.

RNA-Seq of human breast ductal carcinoma in situ models reveals aldehyde dehydrogenase isoform 5A1 as a novel potential target

Breast ductal carcinoma in situ (DCIS) is being found in great numbers of women due to the widespread use of mammography. To increase knowledge of DCIS, we determined the expression changes that are common among three DCIS models (MCF10.DCIS, SUM102 and SUM225) compared to the MCF10A model of non-tumorigenic mammary epithelial cells in three dimensional (3D) overlay culture with reconstituted basement membrane (rBM). Extracted mRNA was subjected to 76 cycles of deep sequencing (RNA-Seq) using Illumina Genome Analyzer GAIIx. Analysis of RNA-Seq results showed 295 consistently differentially expressed transcripts in the DCIS models. These differentially expressed genes encode proteins that are associated with a number of signaling pathways such as integrin, fibroblast growth factor and TGFβ signaling, show association with cell-cell signaling, cell-cell adhesion and cell proliferation, and have a notable bias toward localization in the extracellular and plasma membrane compartments. RNA-Seq data was validated by quantitative real-time PCR of selected differentially expressed genes. Aldehyde dehydrogenase 5A1 (ALDH5A1) which is an enzyme that is involved in mitochondrial glutamate metabolism, was over-expressed in all three DCIS models at both the mRNA and protein levels. Disulfiram and valproic acid are known to inhibit ALDH5A1 and are safe for chronic use in humans for other disorders. Both of these drugs significantly inhibited net proliferation of the DCIS 3D rBM overlay models, but had minimal effect on MCF10A 3D rBM overlay models. These results suggest that ALDH5A1 may play an important role in DCIS and potentially serve as a novel molecular therapeutic target.

MAME models for 4D live-cell imaging of tumor: microenvironment interactions that impact malignant progression

We have developed 3D coculture models, which we term MAME (mammary architecture and microenvironment engineering), and used them for live-cell imaging in real-time of cell:cell interactions. Our overall goal was to develop models that recapitulate the architecture of preinvasive breast lesions to study their progression to an invasive phenotype. Specifically, we developed models to analyze interactions among pre-malignant breast epithelial cell variants and other cell types of the tumor microenvironment that have been implicated in enhancing or reducing the progression of preinvasive breast epithelial cells to invasive ductal carcinomas. Other cell types studied to date are myoepithelial cells, fibroblasts, macrophages and blood and lymphatic microvascular endothelial cells. In addition to the MAME models, which are designed to recapitulate the cellular interactions within the breast during cancer progression, we have developed comparable models for the progression of prostate cancers. Here we illustrate the procedures for establishing the 3D cocultures along with the use of live-cell imaging and a functional proteolysis assay to follow the transition of cocultures of breast ductal carcinoma in situ (DCIS) cells and fibroblasts to an invasive phenotype over time, in this case over twenty-three days in culture. The MAME cocultures consist of multiple layers. Fibroblasts are embedded in the bottom layer of type I collagen. On that is placed a layer of reconstituted basement membrane (rBM) on which DCIS cells are seeded. A final top layer of 2% rBM is included and replenished with every change of media. To image proteolysis associated with the progression to an invasive phenotype, we use dye-quenched (DQ) fluorescent matrix proteins (DQ-collagen I mixed with the layer of collagen I and DQ-collagen IV mixed with the middle layer of rBM) and observe live cultures using confocal microscopy. Optical sections are captured, processed and reconstructed in 3D with Volocity visualization software. Over the course of 23 days in MAME cocultures, the DCIS cells proliferate and coalesce into large invasive structures. Fibroblasts migrate and become incorporated into these invasive structures. Fluorescent proteolytic fragments of the collagens are found in association with the surface of DCIS structures, intracellularly, and also dispersed throughout the surrounding matrix. Drugs that target proteolytic, chemokine/cytokine and kinase pathways or modifications in the cellular composition of the cocultures can reduce the invasiveness, suggesting that MAME models can be used as preclinical screens for novel therapeutic approaches.

3D/4D functional imaging of tumor-associated proteolysis: impact of microenvironment

Proteases play causal roles in many aspects of the aggressive phenotype of tumors, yet many of the implicated proteases originate from tumor-associated cells or from responses of tumor cells to interactions with other cells. Therefore, to obtain a comprehensive view of tumor proteases, we need to be able to assess proteolysis in tumors that are interacting with their microenvironment. As this is difficult to do in vivo, we have developed functional live-cell optical imaging assays and 3D and 4D (i.e., 3D over time) coculture models. We present here a description of the probes used to measure proteolysis and protease activities, the methods used for imaging and analysis of proteolysis and the 3D and 4D models used in our laboratory. Of course, all assays have limitations; however, we suggest that the techniques discussed here will, with attention to their limitations, be useful as a screen for drugs to target the invasive phenotype of tumors.

Aborted autophagy and nonapoptotic death induced by farnesyl transferase inhibitor and lovastatin

Exposure of the human malignant peripheral nerve sheath tumor cell lines STS-26T, ST88-14, and NF90-8 to nanomolar concentrations of both lovastatin and farnesyl transferase inhibitor (FTI)-1 but not to either drug alone induced cell death. ST88-14 and NF90-8 cells underwent apoptosis, yet dying STS-26T cells did not. FTI-1 cotreatment induced a strong and sustained autophagic response as indicated by analyses of microtubule-associated protein-1 light chain 3 (LC3)-II accumulation in STS-26T cultures. Extensive colocalization of LC3-positive punctate spots was observed with both lysosome-associated membrane protein (LAMP)-1 and LAMP-2 (markers of late endosomes/lysosomes) in solvent or FTI-1 or lovastatin-treated STS-26T cultures but very little colocalization in lovastatin/FTI-1-cotreated cultures. The absence of colocalization in the cotreatment protocol correlated with loss of LAMP-2 expression. Autophagic flux studies indicated that lovastatin/FTI-1 cotreatment inhibited the completion of the autophagic program. In contrast, rapamycin induced an autophagic response that was associated with cytostasis but maintenance of viability. These studies indicate that cotreatment of STS-26T cells with lovastatin and FTI-1 induces an abortive autophagic program and nonapoptotic cell death.

The role of neurofibromin in N-Ras mediated AP-1 regulation in malignant peripheral nerve sheath tumors

Plexiform neurofibromas commonly found in patients with Neurofibromatosis type I (NF1) have a 5% risk of being transformed into malignant peripheral nerve sheath tumors (MPNST). Germline mutations in the NF1 gene coding for neurofibromin, which is a Ras GTPase activating protein (RasGAP) and a negative regulator of Ras, result in an upregulation of the Ras pathway. We established a direct connection between neurofibromin deficiency and downstream effectors of Ras in cell lines from MPNST patients by demonstrating that knockdown of NF1 expression using siRNA in a NF1 wild type MPNST cell line, STS-26T, activates the Ras/ERK1,2 pathway and increases AP-1 binding and activity. We believe this is the first time the transactivation of AP-1 has been linked directly to neurofibromin deficiency in a disease relevant MPNST cell line. Previously, we have shown that N-Ras is constitutively activated in cell lines derived from independent MPNSTs from NF1 patients. We therefore sought to analyze the role of the N-Ras pathway in deregulating AP-1 transcriptional activity. We show that STS-26T clones conditionally expressing oncogenic N-Ras show increased phosphorylated ERK1,2 and phosphorylated JNK expression concomitant with increased AP-1 activity. MAP kinase pathways (ERK1,2 and JNK) were further examined in ST88-14, a neurofibromin-deficient MPNST cell line. The basal activity of ERK1,2 but not JNK was found to increase AP-1 activity. These experiments further confirmed the link between the loss of neurofibromin and increased activity of Ras/MAP kinase pathways and the activation of downstream transcriptional mechanisms in MPNSTs from NF1 patients.

A novel geranylgeranyl transferase inhibitor in combination with lovastatin inhibits proliferation and induces autophagy in STS-26T MPNST cells

Prenylation inhibitors have gained increasing attention as potential therapeutics for cancer. Initial work focused on inhibitors of farnesylation, but more recently geranylgeranyl transferase inhibitors (GGTIs) have begun to be evaluated for their potential antitumor activity in vitro and in vivo. In this study, we have developed a nonpeptidomimetic GGTI, termed GGTI-2Z [(5-nitrofuran-2-yl)methyl-(2Z,6E,10E)-3,7,11,15-tetramethylhexadeca-2,6,10,14-tetraenyl 4-chlorobutyl(methyl)phosphoramidate], which in combination with lovastatin inhibits geranylgeranyl transferase I (GGTase I) and GGTase II/RabGGTase, without affecting farnesylation. The combination treatment results in a G(0)/G(1) arrest and synergistic inhibition of proliferation of cultured STS-26T malignant peripheral nerve sheath tumor cells. We also show that the antiproliferative activity of drugs in combination occurs in the context of autophagy. The combination treatment also induces autophagy in the MCF10.DCIS model of human breast ductal carcinoma in situ and in 1c1c7 murine hepatoma cells, where it also reduces proliferation. At the same time, there is no detectable toxicity in normal immortalized Schwann cells. These studies establish GGTI-2Z as a novel geranylgeranyl pyrophosphate derivative that may work through a new mechanism involving the induction of autophagy and, in combination with lovastatin, may serve as a valuable paradigm for developing more effective strategies in this class of antitumor therapeutics.

Three-dimensional overlay culture models of human breast cancer reveal a critical sensitivity to mitogen-activated protein kinase kinase inhibitors

Tumor cells that are grown in three-dimensional (3D) cell culture exhibit relative resistance to cytotoxic drugs compared with their response in conventional two-dimensional (2D) culture. We studied the effects of targeted agents and doxorubicin on 2D and 3D cultures of human breast cell lines that represent the progression from normal epithelia (modeled by MCF10A cells) through hyperplastic variants to a dysplastic/carcinoma phenotype (MCF10.DCIS cells), variants transformed by expression of activated Ras, and also a basal-subtype breast carcinoma cell line (MDA-MB-231). The results showed the expected relative resistance to the cytotoxic agent doxorubicin in 3D cultures, with greater resistance in normal and hyperplastic cells than in carcinoma models. However, the response to the targeted inhibitors was more complex. Inhibition of mitogen-activated protein kinase kinase (MEK) by either 1,4-diamino-2,3-dicyano-1,4-bis(methylthio)butadiene (U0126) or 2-(2-chloro-4-iodo-phenylamino)-N-cyclopropylmethoxy-3,4-difluoro-benzamide (CI-1040, PD184352) produced a similar inhibition of the growth of all the MCF10 cell lines in 2D. In 3D culture, the normal and hyperplastic models exhibited some resistance, whereas the carcinoma models became far more sensitive to MEK inhibition. Increased sensitivity to MEK inhibition was also seen in MDA-MB-231 cells grown in 3D compared with 2D. In contrast, inhibition of phosphatidylinositol 3'-kinase activity by wortmannin had no significant effect on the growth of any of the cells in either 2D or 3D. Our conclusion is that 3D culture models may not only model the relative resistance of tumor cells to cytotoxic therapy but also that the 3D approach may better identify the driving oncogenic pathways and critical targeted inhibitors that may be effective treatment approaches.

Working together: Farnesyl transferase inhibitors and statins block protein prenylation

Farnesyl transferase inhibitors (FTIs) have so far proved to have limited value as single agents in clinical trials. This PharmSight will focus on the use of a novel group of FTIs that are most effective in vitro when used in combination with the "statin" class of anti-hypercholesterolemic agents, which also block protein prenylation. We recently showed that these novel FTIs in combination with lovastatin reduce Ras prenylation and induce an apoptotic response in malignant peripheral nerve sheath cells. The combination of statins with these new FTIs may produce profound synergistic cytostatic and cytotoxic effects against a variety of tumors and other proliferative disorders. Since statins are well tolerated in the clinic, we suggest that this combination approach should be tested in in vivo models.

Suppression of proliferation of two independent NF1 malignant peripheral nerve sheath tumor cell lines by the pan-ErbB inhibitor CI-1033

Neurofibromatosis Type 1 (NF1) is characterized by the abnormal proliferation of neuroectodermal tissues and the development of certain tumors, particularly neurofibromas, which may progress into malignant peripheral nerve sheath tumors (MPNSTs). Effective pharmacological therapy for the treatment of NF1 tumors is currently unavailable and the prognosis for patients with MPNSTs is poor. Loss of neurofibromin correlates with increased expression of the epidermal growth factor receptor (EGFR) and ErbB2 tyrosine kinases and these kinases have been shown to promote NF1 tumor-associated pathologies in vivo. We show here that while NF1 MPNST cells have higher EGFR expression levels and are more sensitive to EGF when compared to a non-NF1 MPNST cell line, the ability of the EGFR inhibitor gefitinib to selectively inhibit NF1 MPNST cell proliferation is marginal. We also show that NF1 MPNST proliferation correlates with activated ErbB2 and can be suppressed by nanomolar concentrations of the pan-ErbB inhibitor CI-1033 (canertinib). Consequently, targeting both EGFR and ErbB2 may prove an effective strategy for suppressing NF1 MPNST tumor growth in vivo.

Induction of apoptosis in neurofibromatosis type 1 malignant peripheral nerve sheath tumor cell lines by a combination of novel farnesyl transferase inhibitors and lovastatin

Neurofibromatosis type 1 (NF1) is a genetic disorder that is driven by the loss of neurofibromin (Nf) protein function. Nf contains a Ras-GTPase-activating protein domain, which directly regulates Ras signaling. Numerous clinical manifestations are associated with the loss of Nf and increased Ras activity. Ras proteins must be prenylated to traffic and functionally localize with target membranes. Hence, Ras is a potential therapeutic target for treating NF1. We have tested the efficacy of two novel farnesyl transferase inhibitors (FTIs), 1 and 2, alone or in combination with lovastatin, on two NF1 malignant peripheral nerve sheath tumor (MPNST) cell lines, NF90-8 and ST88-14. Single treatments of 1, 2, or lovastatin had no effect on Ras prenylation or MPNST cell proliferation. However, low micromolar combinations of 1 or 2 with lovastatin (FTI/lovastatin) reduced Ras prenylation in both MPNST cell lines. Furthermore, this FTI/lovastatin combination treatment reduced cell proliferation and induced an apoptotic response as shown by morphological analysis, procaspase-3/-7 activation, loss of mitochondrial membrane potential, and accumulation of cells with sub-G(1) DNA content. Little to no detectable toxicity was observed in normal rat Schwann cells following FTI/lovastatin combination treatment. These data support the hypothesis that combination FTI plus lovastatin therapy may be a potential treatment for NF1 MPNSTs.

Angiotensin II stimulates elution of Na-K-ATPase from a digoxin-affinity column by increasing the kinetic response to ligands that trigger the decay of E2-P

We earlier observed that treating rat proximal tubules with concentrations of angiotensin II (ANG II) that directly stimulate Na-K-ATPase activity changed how Na-K-ATPase subsequently eluted from an ouabain-affinity column. In this study we tested whether ANG II increases the rate of elution in response to ligands that trigger the decay of E(2)-P, which implies a change in functional properties of Na-K-ATPase, or by decreasing the amount subsequently eluted with SDS, which suggests a change in how Na-K-ATPase interacts with other proteins. We utilized a new digoxin-affinity column and novel lines of opossum kidney (OK) cells that coexpress the rat AT(1a) receptor and either the wild-type rat alpha(1)-isoform of Na-K-ATPase or a truncation mutant missing the first 32 amino acids of its NH(2) terminus. We characterized how rat kidney microsomes bind to and elute from the digoxin-affinity column and demonstrated that they are heterogeneous in the rate at which they release digoxin in response to ligands that trigger the decay of E(2)-P. Incubating OK cells with ANG II stimulated the ensuing elution of wild-type rat alpha(1)-subunit by increasing the kinetic response to ligands that cause a decay of E(2)-P without affecting the amount later eluted with SDS. In contrast, ANG II had no effect on the kinetic response of the truncation mutant but decreased the amount eluted with SDS. These data suggest that ANG II regulates both the kinetic properties of Na-K-ATPase and its interaction with other proteins by a mechanism(s) involving its NH(2) terminus.

Low and nontoxic inorganic mercury burdens attenuate BCR-mediated signal transduction

The ubiquitous environmental heavy metal contaminant mercury (Hg) is a potent immunomodulator that has been implicated as a factor contributing to autoimmune disease. However, the mechanism(s) whereby Hg initiates or perpetuates autoimmune responses, especially at the biochemical/molecular level, remain poorly understood. Recent work has established a relationship between impaired B-cell receptor (BCR) signal strength and autoimmune disease. In previous studies, we have shown that in mouse WEHI-231 B cells, noncytotoxic concentrations of inorganic mercury (Hg(+2)) interfered with BCR-mediated growth control, suggesting that BCR signal strength was impaired by Hg(+2). Extracellular signal-regulated kinase (ERK) 1,2 mitogen-activated protein kinase (MAPK) is responsible for the activation of several transcription factors in B cells. Phosphorylation of ERK serves as an essential node of signal integration for the BCR. Thus, the magnitude of ERK activation serves as an operational metric for BCR signal strength. Using Western blotting and phospho-specific flow cytometry, we now show that the kinetics and magnitude of BCR-mediated activation of ERK-MAPK are markedly attenuated in WEHI-231 cells and splenic B cells that have been exposed to low and nontoxic burdens of Hg(+2). However, Hg(+2) does not seem to act directly on ERK-MAPK but rather on an upstream element or elements of the BCR signal transduction pathway, above the level of the key protein tyrosine kinase Syk. Our data suggest that the site of action of Hg(+2) may very well be localized on the plasma membrane. These findings support a connection between Hg(+2) and attenuated BCR signal strength in the etiology of autoimmune disease.

Synthesis, biochemical, and cellular evaluation of farnesyl monophosphate prodrugs as farnesyltransferase inhibitors

Certain farnesyl diphosphate (FPP) analogs are potent inhibitors of the potential anticancer drug target protein farnesyltransferase (FTase), but these compounds are not suitable as drug candidates. Thus, phosphoramidate prodrug derivatives of the monophosphate precursors of FPP-based FTase inhibitors have been synthesized. The monophosphates themselves were significantly more potent inhibitors of FTase than the corresponding FPP analogs. The effects of the prodrug 5b (a derivative of 3-allylfarnesyl monophosphate) have been evaluated on prenylation of RhoB and on the cell cycle in a human malignant schwannoma cell line (STS-26T). In combination treatments, 1-3 microM 5b plus 1 microM lovastatin induced a significant inhibition of RhoB prenylation, and a combination of these drugs at 1 microM each also resulted in significant cell cycle arrest in G1. Indeed, combinations as low as 50 nM lovastatin + 1 microM 5c or 250 nM lovastatin + 50 nM 5c were highly cytostatic in STS-26T cell culture.

Epac- and Rap- independent ERK1/2 phosphorylation induced by Gs-coupled receptor stimulation in HEK293 cells

Serotonin activates Ras and Ras-dependent ERK1/2 phosphorylation in HEK293 cells expressing G(s)-coupled 5-HT(4) or 5-HT(7) serotonin receptors through unknown mechanisms. Both Epac/Rap-dependent and -independent pathways for Ras-dependent ERK1/2 activation have been suggested. Epac overexpression or Epac-specific 8-CPT-2'-O-Me-cAMP did not cause ERK1/2 phosphorylation, despite Rap activation. The data did not support a role for PLCepsilon or DAG-dependent Ras GEFs of the Ras-GRP family in Ras-dependent ERK1/2 phosphorylation. However, serotonin stimulated phosphorylation of endogenous and recombinant Ras-GRF1, increased [Ca(2+)](i) and caused Ca(2+)- and calmodulin-dependent ERK1/2 phosphorylation. Different signalling pathways seem to be utilised by G(s)-coupled receptors in various isolates of HEK293 cells.

Molecular targets for emerging anti-tumor therapies for neurofibromatosis type 1

Neurofibromatosis type 1 (NF1) is the most common cancer predisposition syndrome. NF1 patients present with a constellation of clinical manifestations and have an increased risk of developing certain benign and malignant tumors. This disease results from mutation within the gene encoding neurofibromin, a GTPase activating protein (GAP) for Ras. Functional loss of this protein compromises Ras inactivation, which leads to the aberrant growth and proliferation of neural crest-derived cells and, ultimately, tumor formation. Current management of NF1-associated malignancy involves radiation, surgical excision, and cytotoxic drugs. The limited success of these strategies has fueled researchers to further elucidate the molecular changes that drive tumor formation and progression. This discussion will highlight how intracellular signaling molecules, cell-surface receptors, and the tumor microenvironment constitute potential therapeutic targets, which may be relevant not only to NF1-related malignancy but also to other human cancers.

The Ras-GRF1 exchange factor coordinates activation of H-Ras and Rac1 to control neuronal morphology

The Ras-GRF1 exchange factor has regulated guanine nucleotide exchange factor (GEF) activity for H-Ras and Rac1 through separate domains. Both H-Ras and Rac1 activation have been linked to synaptic plasticity and thus could contribute to the function of Ras-GRF1 in neuronal signal transduction pathways that underlie learning and memory. We defined the effects of Ras-GRF1 and truncation mutants that include only one of its GEF activities on the morphology of PC12 phaeochromocytoma cells. Ras-GRF1 required coexpression of H-Ras to induce morphological effects. Ras-GRF1 plus H-Ras induced a novel, expanded morphology in PC12 cells, which was characterized by a 10-fold increase in soma size and by neurite extension. A truncation mutant of Ras-GRF1 that included the Ras GEF domain, GRFdeltaN, plus H-Ras produced neurite extensions, but did not expand the soma. This neurite extension was blocked by inhibition of MAP kinase activation, but was independent of dominant-negative Rac1 or RhoA. A truncation mutant of Ras-GRF1 that included the Rac GEF domains, GRFdeltaC, produced the expanded phenotype in cotransfections with H-Ras. Cell expansion was inhibited by wortmannin or dominant-negative forms of Rac1 or Akt. GRFdeltaC binds H-Ras.GTP in both pulldown assays from bacterial lysates and by coimmunoprecipitation from HEK293 cells. These results suggest that coordinated activation of H-Ras and Rac1 by Ras-GRF1 may be a significant controller of neuronal cell size.

Inorganic mercury inhibits the activation of LAT in T-cell receptor-mediated signal transduction

Little is known as to the molecular mechanisms involved with mercury intoxication at very low levels. Although the mechanism is not known, animal studies have nevertheless shown that low levels of mercury may target the immune system. Inorganic mercury (Hg2+) at very low (but non-toxic) levels can disrupt immune system homeostasis, in that genetically susceptible rodents develop idiosyncratic autoimmune disease, which is associated with defective T-cell function. T lymphocyte function is intimately coupled to the T-cell receptor. We have previously reported that on a molecular level, low concentrations of Hg2+ disrupt signaling from the T-cell receptor by interfering with activation of Ras and ERK MAP kinase. In this report we expand upon those results by showing that in T lymphocytes exposed to low concentration of Hg2+, Ras fails to become properly activated because upstream of Ras in the T cell signal transduction pathway, the important scaffolding element Linker for Activation of T Cells (LAT) fails to become properly phosphorylated. Hypo-phosphorylation of LAT occurs, because upstream of LAT, the LAT reactive tyrosine kinase ZAP-70 is also not properly activated in Hg2+ treated cells.

The Mitogen-Activated Protein Kinase/Extracellular Signal-Regulated Kinase Kinase Inhibitor PD184352 (CI-1040) Selectively Induces Apoptosis in Malignant Schwannoma Cell Lines

Type 1 neurofibromatosis (NF1) is a common autosomal dominant disorder that results in neuroectodermal tumors. The NF1 tumor-suppressor gene encodes neurofibromin, which includes a GTPase-activating domain for Ras inactivation. Affinity purification showed N-Ras to be the predominant activated isoform of Ras in two independent neurofibrosarcoma cell lines from NF1 patients (lines ST88-14 and NF90-8). These NF1 cells also demonstrated increased constitutive activity of the extracellular signal-regulated kinases 1 and 2 (ERK1,2) mitogen-activated protein (MAP) kinases compared with a sporadic malignant schwannoma cell line that maintains neurofibromin expression (STS-26T). Thus, MAP kinase kinase (MEK) inhibitors may be a rational approach to NF1 therapy. The MEK inhibitors PD98059 [2'-amino-3'-methoxyflavone], PD184352 (also called CI-1040) [2-(2-chloro-4-iodo-phenylamino)-N-cyclopropylmethoxy-3,4-difluoro-benzamide], and U0126 [1,4-diamino-2,3-dicyano-1,4-bis(2-aminophenylthio)butadiene] all produced concentration-dependent suppression of the proliferation of the three cell lines. Individual MEK inhibitors had similar effects in all three cell lines. However, only the antiproliferative effects of PD184352 correlated closely with the elimination of ERK1,2 MAP kinase activities. PD98059 was primarily cytostatic, whereas U0126 and PD184352 were cytotoxic. Only PD184352 induced apoptosis in all three lines, as indicated by morphology, activation of DEVDase, procaspase-3 cleavage, and the appearance of populations having sub-G(0)/G(1) DNA contents. The differential effects of the MEK inhibitors on cell survival were not dependent on p53 status or effects on the ERK5 pathway. PD184352 was also proapoptotic to primary rat Schwann cells. Hence, although PD184352 effectively killed neurofibrosarcoma cells, its effects on normal Schwann cells may limit its usefulness in the clinic.

Active p21-activated kinase 1 rescues MCF10A breast epithelial cells from undergoing anoikis

The protein kinase, PAK1, is overexpressed in human breast cancer and may contribute to malignancy through induction of proliferation and invasiveness. In this study, we examined the role of PAK1 in the survival of detached MCF10A breast epithelial cells to test whether it may also regulate the early stages of neoplasia. MCF10A cells undergo anoikis, as measured by the cleavage of caspase 3 and poly(ADP-ribose) polymerase (PARP), after more than 8 hours of detachment. Endogenous Akt, PAK1, and BAD are phosphorylated in attached MCF10A cells, but these phosphorylation events are all lost during the first 8 hours of detachment. Expression of constitutively active PAK1 or Akt suppresses the cleavage of caspase 3 and PARP in detached MCF10A cells. Co-overexpression of active PAK1 with dominant-negative Akt, or of active Akt with dominant-negative PAK1, still suppresses anoikis. Thus, Akt and PAK1 enhance survival through pathways that are at least partially independent. PAK1-dependent regulation of anoikis is likely to occur early in the apoptotic cascade as expression of dominant-negative PAK1 increased the cleavage of the upstream caspase 9, while constitutively active PAK1 inhibited caspase 9 activation. These results support a role for activated PAK1 in the suppression of anoikis in MCF10A epithelial cells.

Endogenous expression and protein kinase A-dependent phosphorylation of the guanine nucleotide exchange factor Ras-GRF1 in human embryonic kidney 293 cells

We have previously reported the Ras-dependent activation of the mitogen-activated protein kinases p44 and p42, also termed extracellular signal-regulated kinases (ERK)1 and 2 (ERK1/2), mediated through Gs-coupled serotonin receptors transiently expressed in human embryonic kidney (HEK) 293 cells. Whereas Gi- and Gq-coupled receptors have been shown to activate Ras through the guanine nucleotide exchange factor (GEF) called Ras-GRF1 (CDC25Mm) by binding of Ca2+/calmodulin to its N-terminal IQ domain, the mechanism of Ras activation through Gs-coupled receptors is not fully understood. We report the endogenous expression of Ras-GRF1 in HEK293 cells. Serotonin stimulation of HEK293 cells transiently expressing Gs-coupled 5-HT7 receptors induced protein kinase A-dependent phosphorylation of the endogenous human Ras-GRF1 on Ser927 and of transfected mouse Ras-GRF1 on Ser916. Ras-GRF1 overexpression increased basal and serotonin-stimulated ERK1/2 phosphorylation. Mutations of Ser916 inhibiting (Ser916Ala) or mimicking (Ser916Asp/Glu) phosphorylation did not alter these effects. However, the deletion of amino acids 1-225, including the Ca2+/calmodulin-binding IQ domain, from Ras-GRF1 reduced both basal and serotonin-stimulated ERK1/2 phosphorylation. Furthermore, serotonin treatment of HEK293 cells stably expressing 5-HT7 receptors increased [Ca2+]i, and the serotonin-induced ERK1/2 phosphorylation was Ca2+-dependent. Therefore, both cAMP and Ca2+ may contribute to the Ras-dependent ERK1/2 activation after 5-HT7 receptor stimulation, through activation of a guanine nucleotide exchange factor with activity towards Ras.

Cell surface receptors activate p21-activated kinase 1 via multiple Ras and PI3-kinase-dependent pathways

p21-activated kinases (PAKs) were the first identified mammalian members of a growing family of Ste20-like serine-threonine protein kinases. In this study, we show that PAK1 can be stimulated by carbachol, lysophosphatidic acid (LPA), epidermal growth factor (EGF), and phorbol 12-myristate 13-acetate (PMA) by multiple independent and overlapping pathways. Dominant-negative Ras, Rac, and Cdc42 inhibited PAK1 activation by all of these agonists, while active Rac1 and Cdc42 were sufficient to maximally activate PAK1 in the absence of any treatment. Active Ras induced only a weak activation of PAK1 that could be potentiated by muscarinic receptor stimulation. Studies using inhibitors of the EGF receptor tyrosine kinase, phosphatidylinositol 3-kinase (PI3-kinase) and protein kinase C (PKC) revealed that all of the cell surface agonists could activate PAK1 through pathways independent of PKC, that EGF stimulated a PI3-kinase dependent pathway to stimulate PAK1, and that muscarinic receptor stimulation of PAK1 was predominantly mediated through this EGF-R-dependent mechanism. Activation of PAK1 by LPA was independent of PI3-kinase and the EGF receptor, but was inhibited by dominant-negative RhoA. These results identify multiple Ras-dependent pathways to activation of PAK1.

Angiotensin II directly stimulates activity and alters the phosphorylation of Na-K-ATPase in rat proximal tubule with a rapid time course

We present evidence that Na-K-ATPase in the rat proximal tubule is directly activated by ANG II much faster than previously observed. Specifically, we show that a 2-min exposure to 0.1 and 1 nM ANG II slowed the rate of intracellular sodium accumulation in response to an increase in extracellular sodium added in the presence of gramicidin D. From these data, we show that ANG II directly stimulates Na-K-ATPase activity at rate-limiting concentrations of intracellular sodium. Under these same conditions, exposing proximal tubules to ANG II altered the amount of 32P incorporated into multiple phosphopeptides generated from a tryptic digest of the alpha-subunit of Na-K-ATPase. Na-K-ATPase was isolated from whole cell lysates by means of a ouabain-affinity column and then separated into its individual subunits by SDS-PAGE. Na-K-ATPase bound to the column in its E2 conformation and was eluted by altering its conformation to E1 using Na+ATP. Na-K-ATPase isolated from cells treated with ANG II eluted more easily from the ouabain-affinity column than Na-K-ATPase isolated from control cells, suggesting that ANG II decreased the affinity of Na-K-ATPase for ouabain. Thus ANG II rapidly stimulated the activity of Na-K-ATPase in 2 min or less by a mechanism that could involve changes in phosphorylation and conformation of Na-K-ATPase. We suggest that the physiological role for rapid direct activation of Na-K-ATPase is greater control of intracellular sodium during sodium reabsorption.

TNF-α-mediated apoptosis in normal human prostate epithelial cells and tumor cell lines

In this study we compared the role of TNF-alpha in the regulation of growth and apoptosis in normal human prostate epithelial cells (NP) and prostate tumor cell lines PC3 and LNCap. The NP and PC3 cells were resistant whereas the LNCap cell line was highly sensitive to TNF-alpha induced growth arrest and apoptosis. The resistance of NP and PC3 cells was mediated via an NF-kB survival pathway as treatment of resistant cells with TNF-alpha was accompanied by phosphorylation of I-kBalpha and translocation of NF-kB to the nucleus. TNF-alpha did not induce phosphorylation of I-kB in the sensitive LNCap cells. The sensitivity of LNCap cells involved a cysteine protease cascade as Z-VAD-CH2 F reversed the sensitivity of LNCap cells and induced resistance to TNF-alpha. The differences in susceptibilities to TNF-alpha induced apoptosis of NP and certain prostate tumor cells offer intriguing possibilities for the treatment of prostate cancer without affecting the normal prostate tissue.

Gβγ subunits stimulate p21-activated kinase 1 (PAK1) through activation of PI3-kinase and Akt but act independently of Rac1/Cdc42

The p21-activated kinase (PAK) family is homologous to the yeast sterile 20 (Ste20) and regulates a wide variety of cellular responses, including cell morphology, proliferation, and survival. In this study we examined the activation of PAK1 by Gbetagamma subunits. Co-transfection of COS7 cells with Gbeta1gamma2 or Gbeta1gamma5 was sufficient to induce agonist-independent activation of PAK1. Expression of dominant/negative Rac, Cdc42, or Ras did not inhibit this Gbetagamma-dependent activation. Wortmannin, which inhibits phosphoinositide 3-kinase (PI3-kinase) activity, and expression of a dominant/negative form of Akt were sufficient to abrogate the activation of PAK1 that was induced by Gbetagamma. These results reveal that stimulation of PAK1 by Gbetagamma can occur via a PI3-kinase and Akt pathway that does not require Rac1 or Cdc42.

Mitogen-activated protein kinase signaling in drug-resistant neuroblastoma cells

Widespread inherent or acquired resistance to cytotoxic drugs is a major limitation to chemotherapy. There are many mechanisms that contribute to such resistance. In neuroblastomas there is evidence that acquired drug resistance may be associated with altered response to growth factor signals. The ubiquitous mitogen-activated protein kinase (MAPk) cascade, which transmits growth factor signals from the cell membrane to the nucleus, provides a principal mechanism for regulation of cell cycle progression and proliferation. We have shown that there is a relationship between acquired drug resistance in human neuroblastoma cells to doxorubicin, a topoisomerase-2 inhibitor, and to MDL-28842, an inhibitor of S-adenosylhomocysteine hydrolase, and reductions in the activation and nuclear translocation of MAPk.